VATICAN CITY -- Pope Benedict XVI left Vatican City for the last time Thursday. He
will return - not as Pope Benedict XVI, but as pope emeritus - a retired
man. Hours later, Benedict became the first pope in about 600 years to
retire.

He emerged late in the afternoon from the
Apostolic Palace, walking with the help of a cane, for a short car ride
to a waiting helicopter that would fly him into the next chapter of his
life.

CBS News correspondent Mark Phillips said the crowd outside the
palace was large, but not huge, perhaps because Benedict failed to ever
garner the sort of public adoration that his predecessor, Pope John Paul
II, did, or perhaps because many of those wishing to bid Benedict
farewell did so the previous day during his last general audience at St.
Peter's Square.

The papal limousine wound its way to the
highest point in the Vatican gardens, on which the helipad sits.
Benedict and a few of his closest aides climbed into the Italian Air
Force helicopter for the short flight to the town of Castel Gandolfo,
about 15 miles away. The sun was just beginning to set over the Roman
skyline as the helicopter's rotors started to spin, and the Vatican
bells chimed.

"Thank you for your love and support. May you always experience the joy
that comes from putting Christ at the centre of your lives."

The account was to be shut down after that, his 39th tweet.

After the short flight from the Vatican to the papal retreat at
Castel Gandolfo, he emerged minutes after arriving onto a balcony
overlooking a square below the residence, which has been used by
pontiffs to escape the heat of Rome for centuries.

"Thank
you for your friendship, for your affection," said Benedict, in his
last public appearance as leader of the Roman Catholic Church. "I will
only be the supreme pontiff of the Catholic Church until 8 p.m. and then
no longer. I will simply be a pilgrim who is starting the last phase of
his pilgrimage on this earth.''

"Thank you and good
night, to everyone, thank you," Benedict concluded, before turning and
walking back into the sprawling complex, disappearing from public eyes.

Benedict is expected to spend about two months at the private
retreat, surrounded by 135 acres of picturesque, private gardens, before
moving into an apartment still being prepared in a convent within the
Vatican campus walls.

At Castel Gandolfo, the Swiss
Guards standing at attention shut the gates of the palazzo shortly after
8 p.m. (2 p.m. Eastern) - the exact moment Benedict's resignation went
into effect - symbolically closing the doors on a papacy whose legacy
will be most marked by the way it ended - a resignation instead of a
death.

The guards in attendance were expected to go off
duty, their service protecting the pope now finished. As CBS News
correspondent Allen Pizzey notes, however, even a former pope remains a
potential target, and the duty of his protection will henceforth be
carried out by Vatican police.

The so-called fisherman's
ring, bearing the official insignia of the Bishop of Rome, Supreme
Pontiff of the Catholic Church of Rome, which has been worn by Benedict
for his entire papacy, will be destroyed. A new version will be cast for
his replacement.

Much speculation has surrounded the
date when the conclave will begin for the cardinals to choose a new
pope. On Thursday, soon after Benedict left the Vatican, Monsignor Carlo
Maria Celli, a papal communications officer, hinted that the date could
be March 11. That could not be immediately confirmed.

Earlier
Thursday, Benedict briefly addressed the 144 cardinals gathered in the
Clementine Hall of the Apostolic Palace, thanking them again for their
support and pledging his "unconditional reverence and obedience" to the
man who becomes his successor.

He then gave a blessing,
and personally greeted each of the cardinals in attendance, shaking
their hands and exchanging a few words as they approached him in turn.
The Vatican said he spent the hours before his departure having lunch
and resting.

On Wednesday, Benedict gave his final
general audience in St. Peter's Square, addressing the faithful as
pontiff for one of the last times, and Pizzey says the normally shy pope
made the most of it - pausing to bless about a half dozen babies thrust
toward him on the Popemobile even before taking the altar.

Benedict
thanked the estimated 150,000 people gathered before him, and said he
was "fully aware" of the seriousness and novelty of the situation his
retirement had presented the Catholic world.

Many of the
cardinals - the so-called princes of the church - who will soon be
tasked with choosing Benedict's successor were in the square to hear him
speak.

Pizzey says Benedict described the job that his
replacement will inherit as being like a ship tossed on stormy seas, a
clear acknowledgement of the difficulties he has faced during his
near-eight-year papacy. He went so far as to say that, at times, it
seemed like "the Lord was sleeping."

From the point when
the doors of Castel Gandolfo closed behind him on Thursday, the Vatican
said Benedict will essentially shrink away into a quiet life of prayer
and meditation.

However, Pizzey notes that while Benedict
will be banned from making public statements in his retirement, it is
widely expected that his successor may take advantage of having someone
nearby with whom to consult on the job at hand.